﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Demo
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("请输入圆的半径");
            double r = double.Parse(System.Console.ReadLine());
            const double π = 3.14;
            double mianJ = π * r * r;
            Console.WriteLine("圆的面积是" + mianJ);

        }
    }
}
